The National Transportation Safety Board is investigating the possibility that an overheated wheel bearing in a rail car may have caused last month’s derailment in New Castle that Norfolk Southern estimates caused $6.1 million in damage to equipment and tracks.

That’s according to a preliminary report from the NTSB on the May 10 freight train that derailed in the Mahoningtown neighborhood as it was headed from Conway, Pennsylvania to Buffalo, New York.

An overheated wheel bearing possibly caused the derailment of another Norfolk Southern Train on February 3 in East Palestine, leading to a fire, and chemical leak.

In the New Castle derailment, three locomotives were pulling 213 cars at about 28 miles per hour when, according to investigators, a so-called “hot box detector” recorded that the bearing on one of the cars reached 253 degrees more than a half hour before that car, and eight cars behind it went off the tracks.

The NTSB says that when temperatures exceed 200°, the crew receives a critical alarm, and is required to stop the train immediately.

Investigators say they found no evidence of an audible alarm being broadcast over the locomotive radio and discovered that the hot box detector’s transducers were attached incorrectly along the tracks, thus reporting the wrong direction in which the train was traveling. “That is, a northbound train would be reported as southbound,” according to the NTSB.

 

Norfolk Southern’s Automatic Train Control system requires an accurate report of train travel direction to interpret hot box data, according to the NTSB.

The derailed equipment included one hazardous material tank car containing paraffin which was not breached.

There were no reported fatalities or injuries.

The NTSB is continuing its investigation.